Coppicing and Pollarding

My moringa trees pollarded for the new year

I recently read a great article about a concept that is new to me: coppicing and pollarding. The concept is that both are methods of pruning trees such that the wood is harvested continuously without damaging the tree. The branches are cut off at a smaller size and used for whatever they are needed for, usually firewood or crafting, like basket weaving. The only difference between the two methods is that coppicing is done at ground level while pollarding leaves a length of trunk that is topped. As far as method, I am assuming the central trunk is cut just above a junction in the first year. After that, multiple branches grow from just below the cut and those are left for several years until they are harvested. 

The more I learn about gardening, the more I realize that soil is a living thing and needs to be fed properly. Think of it like people, but with a longer metabolic cycle. While people's metabolic cycle is measured in days, soil's is measured in years. Adding synthetic fertilizer is like you eating a candy bar (well, crystal meth is probably a better comparison), where you get a quick rush and lots of energy, but then you crash afterwards. Compost is a little better, probably a little more like whole wheat bread. It is still a carb. The body uses it up, just a little slower. Wood, though, wood is the ultimate complex carbohydrate. And I don't just mean that metaphorically. Wood is actually a whole lot of sugar molecules chained together, just like starch. The only real difference is that those chains are a lot harder to break. Good chunks of wood will feed your soil for years and years. 

Coppicing and pollarding seem like a great way to get that wood. So how do you add it to the soil? Just grind it up and mix it in? Well, no. Adding sawdust directly to soil in large amounts can be deleterious to your soil. Surface area is the key. Sawdust and wood chips have a lot of surface area and mushrooms will jump in and take advantage of that, but in doing so they draw the nutrients they need to make that jump. They completely deplete the soil of available nitrogen, which is really bad for the plants.

On the other side of the spectrum, there is burying logs. A log over 8 inches in diameter can feed the soil for decades, but it won't release any nutrition at all for several years and when it does, it releases really slowly. Plus, if you don't plant it deep enough, that large chunk of wood just below the surface looks like a wall to a small plant and suddenly your plants don't have soil deep enough to meet their needs.

How I create garden beds. This one was inoculated
with king stropharia mushrooms

With coppicing and pollarding, you can generate a lot of small branches in the 1-2 inch range. Dug down into the soil, hugelkulture style, can give you soil a long burst of really good nutrition and really help build the soil web of life for 5 or more years. Plus, those branches can be used to grow mushrooms. The usual recommendation is to grow mushrooms on logs over 4 inches in diameter, but smaller logs will work if they are bundled tightly. Better yet, the branches can be inoculated and then buried once the mushrooms have taken hold, giving the gardener the ability to harvest several flushes of mushrooms from their consistently improving garden soil. 

The article mentions oak, hazel, ash, chestnut, and willow as good candidates for coppicing and pollardiing. From my experience, I can say that elm, palo verde, and elm would also be great. If you live in Arizona, scrub oak would be one of the best for coppicing. But there is a tree I have only recently been growing that I think could possibly be the best for this method: moringa. The moringa tree is an insanely fast growing tree. From a seed sprouted indoors in the spring, a moringa tree can reach 12-15 feet in height and have a trunk diameter of 2-3 inches. They are completely intolerant of frost, but in cold climates they grow fast enough to be treated as an annual. In warmer climates, if the root ball can be kept from freezing, they can die all the way back to ground level and grow back bigger each year. I have seen a tree get killed back to the ground by a 20 degree F cold snap, only to grow to over 15 feet tall and have a 3 or 4 inch trunk the next year. Plus, the pods they grow, which taste like asparagus, are only edible on new wood. If the tree is left full size, the pods that grow on old wood will be bitter. As you might imagine, any wood grown by a tree this quickly, isn't very hard. In fact, it about as soft as balsa wood. In the garden, it will probably last 2-3 years. That means that 5 trees could feed you and your garden for years to come. 

Hugelkultur

I have grown many mushroom logs over the years and, like any good composter, hate to throw them away when they are spent. It is still a good source of carbon and minerals and not to be wasted. I usually chop them up roughly and throw them in the compost bin, where they tumble for some time, very slowly getting smaller. When I redo one of the containers in my garden, I find I am often short on soil (due in large part to my dislike of store-bought potting soil), so I throw a chunk or two of the decomposing log into the bottom of the pot to fill space. I figure the log will slowly decompose over several years time. During that time, it will feed the soil and provide a reservoir of nutrients.

Recently, I came upon a method of soil-building called hugelkultur. The basic premise is that decaying wood harbors a great diversity of life. If you see a fallen log in the forest, it is covered with different organisms. The older the wood, the more life there is. So, according to hugelkultur, when building soil, you bury wood in the soil. The wood provides both shelter and food source for a wide variety of life. Over the course of several years, the wood will break down into a rich soil that is full of organic matter and many nutrients.

When a mushroom log is good and spent, the interior is spongy and soft. They are easily chopped up into smaller chunks with a large knife. When putting together a new pot full of soil, I like to put a layer of well-draining material on the bottom, like sand or rocks, and then a layer of roughly chopped spent mushroom logs on top of that. I mix it in well with some good compost and then make sure I have three to six inches of dirt on top of the wood. This gives new plants plenty of room to spread their roots without running into wood immediately. While a plant can push its roots through mostly rotted wood, it may have difficulty with some of the harder portions or if you use fresher wood.

Thus far, I have only found two difficulties with hugelkultur. The first is that rotting wood is low in nitrogen. This means that your soil will most likely be low in nitrogen, too, so other sources, such as blood meal, compost, and nitrogen-fixing plants are a good idea as your soil matures, especially if you are going to be growing plants that need lots of nitrogen, like fruits and vegetables.

The second problem is that wood is high in carbon, which mostly gets converted to carbon dioxide as it decomposes. This is good for your plants, providing a slow, steady supply right where they need it. However, that carbon all takes up space. This means that the level of your soil will slowly drop as time passes, sometimes by several inches. This is great for annual plants, as it gives you lots of room to add compost. However, it can be bad for perennials as they slowly get buried in the compost you have to add.

Overall, though, I really like it as a method for bulking up soil in a new bed or container. I especially recommend it for mushroom growers, like me, who have lots of spent logs laying around that they don’t want to throw away.

Caring For Your Mushroom Log

Okay, let’s say that you have followed my directions from previous posts and you selected the mushroom you wanted to grow and started growing a mushroom log. How do you take care of it? If you live in a humid climate that gets regular rain, that is actually pretty easy. Just put it on the north side of your house where it can catch the rain and rarely gets direct sun. Also, limit exposure to the ground to help keep out the bugs and other forms of contamination. Leaning it against the house or stacking on some cinder blocks works well for this.

If, like me, you live in an arid climate, or you want to keep the log inside, things get a little more tricky. You still want to protect the logs from the sun as much as you can, but you now have the added difficulty of keeping them wet normally. The first method is probably the easiest and works for all mushrooms that are happy growing from vertical surfaces. Get a pot that is slightly larger than the log and as tall as a third to a half of the log. Put in the log and fill it with either pasteurized wood chips or sand. Wood chips will give the log a little more nutrition, but you’ll have to inoculate them as well. I have actually inoculated the chips and let them inoculate the log and it has worked pretty well. From there, you just water the pot, pretty much like you would water a plant. Actually, more like you would water a cactus. Since the mushrooms are growing inside the log and have no leaves, they lose much less water to evaporation than plants. So watering them once a month or so is plenty. Another consideration is whether the pot has a drain in it or not. If you do have a drain, it can be difficult to get enough of the water to soak into the log. If you don’t have a drain, the water in the bottom can stagnate and get smelly. Personally, I prefer no drain, but I have done it both ways successfully.

If you want to up the stakes a little, you can make an ecosystem out of it. Once the mushrooms have had a month or two to work, I like to add a handful of worms to the wood chips and a few plants. The worms will break the wood chips down into a rich compost, which helps the plants grow. The plants will help pull water out of the bottom of the pot. They also make a nice indicator. If the plant is wilted, your mushroom probably also needs water. The plant and mushroom are also complimentary on gasses produced. The mushroom produces a slow, steady stream of carbon dioxide as it breaks down the log, which provides a perfect source of food for the plant. The plant provides a slow, steady supply of oxygen, which is perfect for the mushroom. It all makes for a lovely harmonious system, just like nature intended.

Another way of taking care of your log is to just mist it regularly. A regular, thorough misting will soak into the log and help keep it hydrated. Again, I tend to use plants to help with this process. Epiphytes are plants whose roots prefer to never touch soil, instead living up in trees. They aren’t parasites, though. They get all of their moisture from humidity and rain (or regular mistings in the home) and all of their nutrients come from the air. I particularly like epiphytes in the home because I figure (don’t really have any evidence, but it makes sense to me) that if they get all their nutrients from the air, they are probably pretty good at pulling all kinds of noxious gasses from the air. Most kinds of orchids, most kinds of bromeliads (especially tillandsias), and several kinds of ferns are all epiphytes. You can either glue them to your mushroom log or tie them down with wire. Since both orchids and bromeliads have beautiful flowers and often have wonderful forms, they actually make lovely arrangements, especially if you picked a log with branches to nestle the plants in. By regularly misting your plants, you are also regularly misting the log.

So, to recap, the only hard part about caring for a mushroom log is keeping it watered, but not too soggy. It really won’t have any visible signs of life, so you just need to remember to keep it happy until it is ready to produce fruit. I’ll talk about fruiting your log soon.